Isolation of dissolved organic matter in effluents from sewage treatment plant and evaluation of the influences on its DBPs formation

Abstract

a b s t r a c tDissolved organic matter (DOM) in reclaimed water from a conventional sewage treatment plant was isolated using resin adsorption chromatography technique into six classes: hydrophobic bases (HoB), hydrophobic acids (HoA), hydrophobic neutrals (HoN), hydrophilic bases (HiB), hydrophilic acids (HiA) and hydrophilic neutrals (HiN). It was found that organic acids dominated in reclaimed water and the ratios of UV 254 (absorbance at 254 nm) to dissolved organic carbon (DOC) (SUVA 254 ) ratio exhibited a common relationship: HoA > reclaimed water > HiA. The influences of chemical structures and experimental conditions on the formation of disinfection by-products (DBPs) were investigated, respectively. SUVA 254 was found to exhibit a positive and statistically significant correlation with DBPs formation potential. The specific trihalomethanes (THMs) and haloacetic acids (HAAs) formation potential decreased as the same sequence: acids, neutrals and bases. The formation of DBPs depended more on a combination of aromatic moieties and aliphatic structures such as hydroxy acids. Furthermore, THMs formed more easily at alkaline conditions; however, hydrophobic organics formed HAAs more easily at acidic conditions, whereas hydrophilic organics achieved relatively high HAAs at both acidic and strong alkaline conditions. Moreover, the observed rate constant for HAAs formation was larger than the rate constant for THMs formation. Addition of ammonia nitrogen (NH 4 -N) changed chlorine to chloramines with lower oxidation potential, and correspondingly influenced the formation of DBPs especially at the chlorination breakpoint.

Toxicity assessment of chlorinated secondary effluents by theVibrio fischeribioluminescence assay

“…The one-way ANOVA test displayed a decreasing tendency for EC50 at any considered experiment time with the increase of Cl 2 /NH 4 -N ratios. This fact would suggest a higher DBPs formation, as previously reported by Zhang et al [20]. With the increasing of Cl 2 /NH 4 -N ratios, chlorine or chloramines previously formed would hydrolyze to form hypochlorous acid (HOCl), which would clearly increase DBP formation.…”

“…At low pH values, HOCl is the predominant specie, which is responsible for the formation of DBPs because a higher oxidative capacity than OCl -anion. On the other hand, an increase in pH also enhances the degradation of these DBPs [20,22]. Diehl et al [21] reported similar results, showing a decrease on different DBP formation with an increase in the pH from 6 to 10, and Yang et al [22] found a marked difference in DBP formation in Suwannee river water, as judged by the range in pH from 4 to 9; the maximum yields of DBPs occurred at pH 5-6. For all these reasons, a pH control would contribute to a significant reduction of DBPs formation [23].…”

Ecotoxicological screening of reclaimed disinfected wastewater by Vibrio fischeri bioassay after a chlorination–dechlorination process

“…EC50 for 5, 10, and 15 min exhibited a similar decreasing tendency as Cl 2 to NH 4 + increased. This means that more DBPs are formed at greater Cl 2 :NH 4 + ratios, as also suggested by Zhang et al [27] and Diehl et al [28]. In these conditions, chlorine to chloramines previously formed would hydrolyze to form hypochlorous acid (HOCl) in equilibrium with free chlorine released by this hydrolysis, which would increase DBP formation.…”

“…At low pH values, HOCl is the predominant species, responsible for the formation of DBPs because it has a greater oxidative capacity than the OCl − anion found at greater pH. An increase in pH also enhances the degradation of these DBPs [27,30]. Diehl et al [28] reported similar results, showing a decrease of DBP formation with an increase in the pH from 6 to 10.…”

Coagulation behavior of polyferric chloride for removing NOM from surface water with low concentration of organic matter and its effect on chlorine decay model

“…The raw water had DOC values <3 mg/L which could be regarded as water with low concentration of OM. Based on the SUVA measurements (less than 3 L/(mg m)), the NOM in the raw water was hydrophilic, with low molecular weight [27,28].…”